The invention relates to a system for providing a vehicle with in-flight attitude control and side-force steering, also known as a divert and attitude control system (DACS).
The invention is particularly applicable to the high or terminal portions of interceptor missiles used for defense against ballistic missiles, and specifically to maintaining a desired trajectory and attitude at the end of a mission. Nevertheless, the invention can be used for other types of air or space vehicle, e.g. for anti-aircraft defense missiles, air-to-air missiles, atmospheric reentry vehicles, or indeed space exploration modules.
A known DACS for a vehicle constituting the terminal portion of an interceptor missile is shown very diagrammatically in FIG. 1. This DACS 1 comprises a thruster body 2 having two propellant blocks 3 ideally arranged on either side of a metal ring 4 carrying side-force steering or trajectory divert valves 5. Four divert valves 5 are provided, and they are arranged regularly around the axis A of the vehicle 1, substantially level with its center of gravity, so as to generate side thrusts perpendicularly to the axis A without major disturbance to the attitude of the vehicle 1. Six other valves 6 for attitude correction are provided at the rear end of the thruster body 2. These attitude control system (ACS) valves 6 comprise a first pair of valves having two valves oriented in a first direction substantially perpendicular to the axis A, a second pair of valves having two valves oriented in a second direction opposite to the first direction, and two other valves oriented in mutually opposite directions that are substantially perpendicular to the axis A and to the first and second directions. A control device (not shown) comprising control electronics and actuators is provided for selectively controlling the opening of one or two valves 5 when a trajectory correction is needed, and for selectively opening one or more valves 6 when an attitude correction is required (a correction in yaw, roll, and/or pitching). The propellant blocks 3 are used simultaneously for feeding the valves 5 and 6.
Such a configuration for a DACS requires a total of ten valves arranged in two groups having distinct functions, the trajectory divert valves and the attitude control valves generally being of different types, with this being penalizing in terms of weight, size, and cost. In addition, the location of the divert valves within the thruster body and between two blocks of propellant is not optimal in terms of pyrotechnic safety, in particular during assembly operations, and it makes control and maintenance of the propulsive system more complex. Furthermore, the location of the divert valves limits operation duration because they are exposed to very high temperatures, or else puts a limit on gas temperature, and in either case performance suffers.
Other DACSs are described in document GB 2 251 834 A.
In one embodiment, two sets of four valves are arranged on opposite sides of the center of gravity of the vehicle. In each of the sets, two valves exert thrust in a first direction and two other valves exert thrust in a second direction opposite to the first, the thrust axes of the valves being situated at a distance from the longitudinal axis of the vehicle, on either side thereof.
Such a system makes it possible at any given instant to divert the trajectory solely along the thrust axes of the valves. In order to divert the trajectory in some other direction, it is necessary to begin by orienting the missile about its own axis by using its ability to control its attitude in roll. This leads to a loss in response time and in maneuverability, and also to significant excess consumption. The same applies in particular for performing a yaw correction.
In another embodiment, two sets of four valves are likewise arranged on opposite sides of the center of gravity of the vehicle. In each set, two valves exert thrust in opposite directions in alignment on a common first axis and two other valves exert thrust in opposite directions in alignment on a common second axis, the first and second axes being mutually perpendicular and being perpendicular to the axis of the vehicle, and intersecting on the axis of the vehicle. Roll control is therefore not possible.